To be honest with the whole subject of this:
I personally think, some of the community is made up of, pretty much, hormone raging kids. They're curious and it's how they let their sexual urges out. I find no problem with it if they do it in PMs or if in Towns, in Houses, preferably their own house but it's whatever. Just not in like... general public. I mean, lovey gestures like " *kisses* " or whatever is alright in public. But the whole sex concept really isn't. I hate it when people complain about them walking in on noobs cybering in a random house. At least they're doing it privately, it's not like they're disturbing you. You're pretty much disturbing them.
I mean, it shouldn't be done at all on this site... but not everyone is going to follow the rules, and they aren't bothering anyone. It may be useless but it's really harmless. I don't get why it's such a big deal when you "walking in on them" is pretty much, overall, disturbing them. If you find them in a house you entered, simply leave and go into another house. If it happens to be yours, just kindly ask them to leave, if they don't then report them. Simple as that.